1. Field of the Invention
The present invention relates to a fuel injection controlling system for a diesel engine. More particularly, it relates to a fuel injection controlling system for not exclusively but preferably a multi-cylinder type diesel engine having an exhaust gas recirculating system (an EGRsystem), i.e., a system used for recirculating a part of the exhaust gas into an intake passage of the multi-cylinder type diesel engine. The recirculated exhaust gas will be hereinafter referred to as EGR gas.
2. Background Information
Generally, in a diesel engine, when an amount of fuel injection is increased, there often occurs a lack of air to be supplied to the engine together with the increased fuel to thereby result in a generation of smoke. Therefore, a limit to the increase in the amount of fuel injection is predetermined as a smoke-generating limit, and a controlling is conducted to prevent an amount of fuel injection from increasing beyond the smoke-generating limit. In other words, an amount of fuel injection is always controlled lest it should exceed a limitative smoke generating fuel injection amount. At this stage, combustion is usually taken place in the diesel engine under such a condition that the air-fuel ratio is somewhat leaner than the stoichiometric air-fuel ratio, that is the amount of the intake air into the diesel engine is somewhat larger than that necessary for constituting the stoichiometric air-fuel ratio. Thus, a part of the fresh intake air remains in the EGR gas while permitting some amount of residue oxygen gas to be left in the EGR gas. Therefore, a fuel injection controller has been proposed by which computation of the limitative smoke generating fuel injection amount is performed by taking into account the remaining amount of fresh air in the EGR gas, which produces the above-mentioned residue oxygen gas (Japanese laid-open Patent Publication No. 9-242595 should be referred to).
In the fuel injection controller of the prior art, an amount of intake air Qac entering each cylinder (it will be hereinafter referred to as a cylinder intake air) with respect to an amount of air measured by an airflow meter is computed by using approximation of dynamics of air according to a distance from the air-flow meter to the cylinder, made by a primary delay. Similarly, a suction amount Qec of the ERG gas for each cylinder (it will be hereinafter referred to as a cylinder suction amount of ERG gas) is computed by using approximation of dynamics of air according to a distance from an ERG valve to the cylinder (this distance is smaller than the foregoing distance), made by a primary delay. Then, assuming that the residue amount of air within the cylinder suction amount of EGR gas Qec and the afore-mentioned cylinder intake air amount Qac are both used again for the cylinder combustion, the total amount of the fresh intake air per each cylinder (=Qac+Qecxc3x97KOR, where KOR is a constant indicating a ratio of the residue fresh air) is computed. Further, on the basis of the computed total amount of the fresh intake air, the amount of fuel injection determined by a limitative excess coefficient of air is computed to obtain the smoke-generating limit of the fuel injection amount. Thus, when an objective or target amount of fuel injection for each cylinder computed in response to driving conditions of a vehicle exceeds the above-mentioned smoke-generating limit of the fuel injection amount, a controlling is performed so as to suppress the objective amount of fuel injection for each cylinder to the smoke-generating limit of the fuel injection amount.
Nevertheless, unlike a gasoline engine, a diesel engine is constructed and operated so that supply of fuel by injection occurs ahead of supercharging of the air. Thus, when a vehicle mounting thereon the diesel engine is accelerated, the rotating speed of the engine is increased in advance of an increase in the amount of the air due to the supercharging. As a result, the total amount of the fresh air per each cylinder is reduced at an initial stage of the vehicle acceleration. Further, since the airflow meter and the ERG valve are disposed at different positions with regard to the engine, a distance from each cylinder to the airflow meter is different from that from each cylinder to the ERG valve. Thus, when the dynamics of the air is taken into account with respect to the above-mentioned distances from the cylinder to the airflow meter and the ERG valve, the cylinder suction amount of ERG gas Qec is reduced before the cylinder intake air amount Qac is increased. Therefore, the total amount of air as per each cylinder changes so that it is once reduced and thereafter increased. Thus, if the amount of fuel injection is suppressed to the limitative smoke generating amount of the fuel injection which is computed based on the above-mentioned total amount of air as per each cylinder, the suppressed limitative smoke-generating amount of the fuel injection must also change in such a manner that it is temporarily reduced after the fuel injection under a given limitative smoke generating amount of the fuel injection is once carried out, and thereafter it is increased. Therefore, the temporary reduction in the amount of fuel injection during engine acceleration will causes a change in a torque exhibited by the engine, and accordingly an accelerating drivability of a vehicle, especially a vehicle with a manual transmission is deteriorated.
A further description of the prior art fuel injection controller will be provided hereinbelow with reference to FIG. 22.
As shown in FIG. 22, when an accelerator pedal is pressed down at a time t1, a corresponding response occurs rather quickly in the cylinder suction ERG amount Qec by taking into account the dynamics of the air, and terminates at a time t5. However, in comparison with the above-mentioned cylinder suction ERG amount Qec, a response occurs at a later time t3 in the cylinder intake air amount Qac. A difference in the starting times between the respective responses causes a temporary reduction in the total amount of the fresh air as per each cylinder as depicted by a fourth curve from the top in FIG. 22. Thus, when the limitative smoke generating fuel injection amount QSMOKEN in proportion to the above total amount of the fresh air as per each cylinder is computed, a temporary reduction in the limitative smoke-generating fuel injection amount QSMOKEN occurs as depicted by a fifth curve in solid line from the top in FIG. 22. Therefore, if a requested amount of fuel injection (an objective fuel injection amount Qsol1 indicated by a single dotted and dashed line) in compliance with an opening degree of an accelerator system of a vehicle is limited to the limitative smoke-generating fuel injection amount QSMOKEN, the limitative smoke-generating fuel injection amount QSMOKEN corresponds to an actual fuel amount injected into each cylinder. Since an output torque exerted by the engine is in proportion to the actual fuel amount, a temporary reduction appears in the output torque exerted by the engine. As a result, in the case of a vehicle provided with a manual transmission, the temporary reduction in the output torque, that is the torque fluctuation causes an operating shock, i.e., a so-called stumbling which is unfavorable to a vehicle driver and/or a passenger.
In the case of a vehicle provided with a torque converter, torque fluctuation is absorbed by the torque converter, and accordingly a temporary reduction in the output torque does not provide any adverse affect on the motion of the vehicle. However, when the lockup mechanism is in operation, the vehicle provided with the torque converter may be exposed to the operating shock in a manner similar to the vehicle provided with the manual transmission.
Although the foregoing description of the prior art fuel injection controller is directed to the case where a diesel engine is in its accelerating operation, a like problem such as the stumbling phenomenon and the unfavorable smoke generation appears in the case where the diesel engine is in its another operating condition in which the engine is re-accelerated immediately after being decelerating. Namely, as illustrated in FIG. 23, during the deceleration of the diesel engine, the limitative smoke generating fuel injection amount QSMOKEN temporarily increases on the contrary to the acceleration of the vehicle engine (see a fifth solid line curve from the top of FIG. 23). Nevertheless, the amount of fuel injection Qsol1 is not suppressed by the increase of the limitative smoke generating fuel injection amount QSMOKEN during the decelerating operation of the diesel engine. This is because the limitative smoke generating fuel injection amount QSMOKEN determines the upper limit of the fuel injection amount, but the fuel injection amount Qsol1 does not exceed the upper limit thereof during the deceleration of the diesel engine (a curve Qsol1 with a single dotted and dashed line in FIG. 23 should be referred to). Nevertheless, when the diesel engine is accelerated immediately after the decelerating operation, the limitative smoke generating fuel injection amount QSMOKEN indicates only a temporary increase due to a delay in an intake amount of the fresh air, while the fuel injection amount Qsol1 which is a map value according to the operating conditions of the diesel engine (i.e., an engine rotating speed and the opening degree of the accelerator system), indicates an immediate increase in response to the operating conditions of the diesel engine. Therefore, when the fuel injection amount Qsol1 increases beyond the limitative smoke generating fuel injection amount QSMOKEN due to the engine acceleration immediately after the deceleration, the above-mentioned temporary increase in the limitative smoke generating fuel injection amount QSMOKEN becomes an actual fuel amount injected into each cylinder of the diesel engine. At this stage, it should be noted that although the upper limit of the fuel injection amount varies to become lower, namely, varies so as to suppress smoke generation from the diesel engine during the afore-mentioned accelerating stage, the upper limit of the fuel injection amount varies to become larger, namely, varies so as to degrade smoke generation from the diesel engine during the acceleration immediately after the deceleration to thereby cause not only occurrence of a torque shock but also degradation of the smoke generation due to a temporary increase in the amount of fuel injection.
Accordingly, an object of this invention is to provide a fuel injection controlling system for a diesel engine, which is capable of preventing vehicle accelerating drivability from being degraded when the engine mounted on a vehicle with a manual transmission device is in one of the transient operation stages, more specifically, in an accelerating stage and also when the engine mounted on a vehicle with a torque converter having a lockup mechanism is in an accelerating stage under a locking-up condition.
This object is basically attained by a fuel injection controlling system which is able to store a first limitative smoke generating fuel injection amount at a given judging time during the accelerating operation of the diesel engine, to compare the stored limitative smoke generating fuel injection amount with respective first limitative smoke generating fuel injection amounts computed from time to time even after the given judging time to thereby determine a larger one as a computed second limitative smoke generating fuel injection amount after the given judging time, on the basis of the above comparison, and to regulate an objective amount of fuel injection from the given judging time so as not to exceed the computed second limitative smoke generation fuel injection amount.
Another object of this invention is to provide a fuel injection controlling system for a diesel engine, which is capable of preventing vehicle drivability and smoke generation from the engine from being degraded either when the engine mounted on a vehicle provided with a manual transmission is in another one of the transient operation stages, i.e., an accelerating operation stage immediately after the engine is decelerated or when the engine mounted on a vehicle provided with a torque converter with a lockup mechanism is accelerated immediately after it is decelerated under a lock-up condition.
This object of this invention is attained by a fuel injection controller for a diesel engine which is able to store a first limitative smoke generating fuel injection amount at a given judging time during the decelerating operation of the diesel engine, to compare the stored limitative smoke generating fuel injection amount with respective first limitative smoke generating fuel injection amounts computed from time to time even after the given judging time during the decelerating operation to thereby determine a smaller one as a computed second limitative smoke generating fuel injection amount after the given judging time during the decelerating operation, on the basis of the above, comparison, and to regulate an objective fuel injection amount at a time when an accelerating operation is conducted immediately after the given judging time during the decelerating operation so as not to exceed the computed second limitative smoke generating fuel injection amount from the given judging time during the decelerating operation of the diesel engine.
In accordance with the present invention there is provided a fuel injection controlling system for a diesel engine provided with an intake passage for intake air, a fuel supply system for fuel injected in an engine cylinder, and an EGR passage for exhaust gas recirculation, said fuel injection controlling system comprising:
a sensor unit that detects an amount of intake air through the intake passage, an amount of exhaust gas through the EGR passage, and a transient operation condition of the engine; and
a control unit including a computing unit and a memory unit and operatively connected to the sensor unit for determining an objective amount of fuel wherein the control unit:
computes an amount of intake air entering the engine cylinder based on the detected amount of intake air;
computes a residue amount of fresh air within the detected amount of exhaust gas introduced in the engine cylinder;
obtains a sum of the computed amount of intake air and the computed residue amount of fresh air;
computes a basic limitative amount of fuel that defines a smoke generation limit based on the sum;
detects commencement of the transient operation condition;
stores the basic limitative amount of fuel at the instance in which the commencement of the transient operation condition has been detected;
compares the stored basic limitative amount of fuel to the computed basic limitative amount of fuel to obtain a desired limitative amount of fuel;
prevents the objective amount of fuel from exceeding the desired limitative amount of fuel.
Preferably, in one aspect of the present invention, the above-described fuel injection controlling system for a engine is characterized in that when the judgment of the transient operation of the engine conducted by the control unit comprises an operation for judging whether or not the engine comes into accelerating operation, the control unit compares the stored basic limitative amount of fuel injection with the basic limitative amount of fuel injection computed during the accelerating operation of the engine to thereby determine a larger one of the stored basic limitative amount of fuel injection and the computed basic limitative amount as the desired limitative amount of fuel injection from the time of the judgment of the accelerating operation of the engine, and prevents the objective amount of fuel injection from the time of the judgment of the accelerating operation of the engine from exceeding the desired limitative amount of fuel injection so that the diesel engine is constantly supplied with the objective amount of fuel injection.
Preferably, in another aspect of the present invention, the above-described fuel injection controlling system for a diesel engine is characterized in that when the judgment of the predetermined driving operation of the engine conducted by the control unit is conducted to judge whether or not the engine comes into a decelerating operation, the control unit compares the stored basic limitative amount of fuel injection with the basic limitative amount of fuel injection computed during the decelerating operation of the engine to thereby determine a smaller one of the stored basic limitative amount and computed basic limitative amount of fuel injection as the desired limitative amount of fuel injection from the time of the judgment of the decelerating operation of the engine, and prevents the objective amount of fuel injection from a time of accelerating operation of the engine immediately after the time of the judgment of the decelerating operation of the engine from exceeding the desired limitative amount of fuel injection from the time of the judgment of the decelerating operation of the engine so that the engine cylinder of the diesel engine is constantly supplied with the objective amount of fuel injection.